1. Field of the Invention
The present invention relates to a transmitting apparatus and method of a mobile communication terminal, and more particularly, to a transmitting apparatus and method of a mobile communication terminal capable of correcting power changes due to an impedance change of an antenna and a mismatching of the antenna.
2. Description of the Related Art
In general, an antenna of a mobile communication terminal changes its impedance characteristics depending on its distance from a user, the user's size, or the position the user is using the mobile terminal. Generally, a transmission signal is transmitted after being corrected through an antenna matching unit.
FIG. 1 is a block diagram showing the construction of a related art transmitting apparatus of a mobile communication terminal.
As shown in FIG. 1, the related art transmitting apparatus includes a mixer 2 for up-converting a frequency of a transmission signal inputted through a baseband signal processor 1 and outputting a radio frequency signal; a first amplifier 4 for filtering the high frequency signal outputted from the mixer 1 and amplifying it to a certain level; a second amplifier 6 for amplifying a signal outputted from the first amplifier 4 through a second filter 5; a third filter 8 for filtering a signal inputted through an isolator 7 after being transmitted from the second amplifier 6; a coupler 9 for detecting power of a signal outputted from the third filter 8; an antenna matching unit 10 for correcting a signal outputted through the coupler 9 and transmitting the signal to an antenna 11; and a baseband signal processor 1 for outputting a power control signal according to power of the signal detected by the coupler 9 and controlling the first and second amplifiers 4 and 6 according to the power control signal.
The transmitting apparatus of a mobile communication terminal constructed as described above operates as follows.
The baseband signal processor 1 applies a transmission signal to the mixer 2. The mixer 2 up-converts a frequency of the transmission signal and outputs a radio frequency signal. The first filter 3 restrains generation of a spurious frequency, and a signal outputted from the first filter 3 is amplified to a certain level in the first amplifier 4 and inputted to the second amplifier 6 after passing through the second filter 5.
The second amplifier 6 amplifies the signal received from the second filter 5 to a certain level, and the amplified signal is filtered in the third filter 8 after passing through the isolator 7. The isolator 7 protects the second amplifier 6 from reflection wave generated due to impedance mismatching and prevents load change after the second amplifier 6 to thereby prevent change in output power. The coupler 9 transmits a signal outputted from the third filter 8 to the antenna matching unit 10. The signal transmitted to the antenna matching unit 10 is impedance matched and transmitted externally through the antenna 11.
The coupler 9 divides a portion of the signal outputted from the third filter 8 and transmits the divided portion of the signal to the baseband signal processor 1. Then, the baseband signal processor 1 controls the first amplifier 4 and the second amplifier 6 according to a difference between the power of the signal and the power of the transmission signal, thereby adjusting output power of the transmission signal.
Some mobile communication terminals do not have the isolator 7 due to size and cost limitations. As a result, the impedance change in the antenna produces a load change in the power amplifier. As a result, so the output power of the transmission signal is changed in an undesirable manner. The antenna 11 of the mobile communication terminal is exposed to users and environment and thus, the impedance of the antenna is frequently changed.
The related art transmitting apparatus of the mobile communication terminal has the following problems. Since the level of the signal outputted from the power amplifier changes due to the impedance change of the antenna, power of the transmission signal changes. A signal cannot be radiated with accurate power, as a result, and the communication quality is degraded. In addition, in order to satisfy an electromagnetic wave regulation through an SAR, radiation performance of the antenna is attenuated even in a free space state, so that the impedance is changed and the terminal is mismatched with the antenna frequently.
A solution to the above problems is needed.